Mom knows so much, in fact, that she accompanied her daughter this morning to the opening of the San Francisco Sex Worker Film Festival.

"A mother should stand behind her daughter, whatever she does," said the mother of Scarlot Harlot, a San Francisco prostitute and the director of the three-day festival. "If this makes my daughter happy, I'm for it."

Mom, who asked not to be identified, sat beside Harlot in the lobby of the Roxie Cinema on 16th Street, helping to pass out the festival programs. For the next three days, mother and daughter will preside over such works as "Sex Flesh in Blood," "Bad Girl" and "Bare Bottom Spanking and Salvation."

These may sound like dirty movies but, said Harlot, they aren't. That's because they are made by sex workers themselves, who keep all the profits. The obscene part of most sex movies, said Harlot, is the low wages paid to the artists and the huge cut kept by the middlemen. The rest of it is just showbiz.

Harlot and her mother, a 70ish woman in a black coat who goes by "Mrs. Harlot," are working together on their second sex film festival -- 28 hours of sex documentaries, sex features, sex comedies and other examples of the genre.

"There are 5,000 prostitutes and sex workers in San Francisco, and we make a huge contribution to the economy," Harlot said, while her mother sat alongside, leaning on a cane and nodding. "We spend money in restaurants and stores, and nobody turns us away then. It's so hypocritical."

Harlot, decked out in a simple red sequin pantsuit and understated ostrich feather boa for the festival opening, said the best buy for festival fans is an all-day pass for $25, which buys 14 hours of nonexploitative, politically correct X-rated movies.

The all-day pass includes admission to the awards ceremony tonight, at which some lucky sex worker will take home the coveted spike heel award.

Throughout the festival, Mrs. Harlot will work side by side with her daughter, putting up posters, fluffing the boa and straightening things out as only a mother can.

"I'm a fighter for a woman's right to choose," said Mrs. Harlot, "and this is what my daughter chose."

On Sunday, the movies end and the festival moves around the corner to New College for a high-minded panel discussion on prostitutes' rights, featuring "invited academic presenters" and other people who know what they're talking about.

The festival represents something of a sea change for the Roxie, a high- minded art house where the movies are frequently subtle and subtitled.

"We're glad to host the festival," said Elliot Levine, director of programming at the Roxie. "These women are artists. And we are also very excited about our new Coke machine at the snack bar, which is having its grand opening, too."